Description: This function deletes sets with no nodes assigned to them.
Usage:
1. DSI deletes any empty node sets. If empty node sets are found, DSI shows the number of sets found and prompts:
> OK TO DELETE (1) EMPTY NODE SETS? (Y/N)
If no unreferenced node sets are found, DSI prompts:
> NO EMTPY NODE SETS FOUND
and returns to the node set menu.